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Correctly handle modifying LCR register after uart enable

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This commit is contained in:
Mathias 2024-07-17 12:20:31 +02:00
parent d1207706c0
commit 4c34132337
1 changed files with 51 additions and 22 deletions
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73
embassy-rp/src/uart/mod.rs
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@ -860,6 +860,56 @@ impl<'d, T: Instance + 'd, M: Mode> Uart<'d, T, M> {
});
}
fn lcr_modify<R>(f: impl FnOnce(&mut rp_pac::uart::regs::UartlcrH) -> R) -> R {
let r = T::regs();
// Notes from PL011 reference manual:
//
// - Before writing the LCR, if the UART is enabled it needs to be
// disabled and any current TX + RX activity has to be completed
//
// - There is a BUSY flag which waits for the current TX char, but this is
// OR'd with TX FIFO !FULL, so not usable when FIFOs are enabled and
// potentially nonempty
//
// - FIFOs can't be set to disabled whilst a character is in progress
// (else "FIFO integrity is not guaranteed")
//
// Combination of these means there is no general way to halt and poll for
// end of TX character, if FIFOs may be enabled. Either way, there is no
// way to poll for end of RX character.
//
// So, insert a 15 Baud period delay before changing the settings.
// 15 Baud is comfortably higher than start + max data + parity + stop.
// Anything else would require API changes to permit a non-enabled UART
// state after init() where settings can be changed safely.
let clk_base = crate::clocks::clk_peri_freq();
let cr = r.uartcr().read();
if cr.uarten() {
r.uartcr().modify(|w| {
w.set_uarten(false);
w.set_txe(false);
w.set_rxe(false);
});
// Note: Maximise precision here. Show working, the compiler will mop this up.
// Create a 16.6 fixed-point fractional division ratio; then scale to 32-bits.
let mut brdiv_ratio = 64 * r.uartibrd().read().0 + r.uartfbrd().read().0;
brdiv_ratio <<= 10;
// 3662 is ~(15 * 244.14) where 244.14 is 16e6 / 2^16
let scaled_freq = clk_base / 3662;
let wait_time_us = brdiv_ratio / scaled_freq;
embedded_hal_1::delay::DelayNs::delay_us(&mut Delay, wait_time_us);
}
let res = r.uartlcr_h().modify(f);
r.uartcr().write_value(cr);
res
}
/// sets baudrate on runtime
pub fn set_baudrate(&mut self, baudrate: u32) {
Self::set_baudrate_inner(baudrate);
@ -886,28 +936,7 @@ impl<'d, T: Instance + 'd, M: Mode> Uart<'d, T, M> {
r.uartibrd().write_value(pac::uart::regs::Uartibrd(baud_ibrd));
r.uartfbrd().write_value(pac::uart::regs::Uartfbrd(baud_fbrd));
let cr = r.uartcr().read();
if cr.uarten() {
r.uartcr().modify(|w| {
w.set_uarten(false);
w.set_txe(false);
w.set_rxe(false);
});
// Note: Maximise precision here. Show working, the compiler will mop this up.
// Create a 16.6 fixed-point fractional division ratio; then scale to 32-bits.
let mut brdiv_ratio = 64 * r.uartibrd().read().0 + r.uartfbrd().read().0;
brdiv_ratio <<= 10;
// 3662 is ~(15 * 244.14) where 244.14 is 16e6 / 2^16
let scaled_freq = clk_base / 3662;
let wait_time_us = brdiv_ratio / scaled_freq;
embedded_hal_1::delay::DelayNs::delay_us(&mut Delay, wait_time_us);
}
// PL011 needs a (dummy) line control register write to latch in the
// divisors. We don't want to actually change LCR contents here.
r.uartlcr_h().modify(|_| {});
r.uartcr().write_value(cr);
Self::lcr_modify(|_| {});
}
}